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Hyper-V and Dynamic Memory in Depth

Agenda. Users, Memory

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Hyper-V and Dynamic Memory in Depth

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    1. Benjamin Armstrong Senior Program Manager Lead Microsoft Hyper-V and Dynamic Memory in Depth

    3. Agenda Users, Memory & Virtualization Dynamic Memory Architecture & Concepts System Impact Memory Techniques / Competition

    4. Users, Memory & Virtualization

    5. No one can size VMs How much memory does an IIS server actually need? Print server? File server? Branch Cache? Direct Access? How much will performance be affected if you halved the amount of memory in a VM?

    6. No one wants to size VMs New virtual machines get 1GB of RAM [no matter what the VM is running]. I only give people more memory if they complain about performance All VMs get 4GB of RAM [I have no idea what is happening with that memory] and no one complains I take the minimum system requirements and add (insert one: 50%, 100%, 150%) A vendor tells me their app needs 4GB of RAM. I do not have the time to test this to find out if it is true or not

    7. Memory is a Bottleneck Key factor to the number of running VMs Possibly most expensive asset in system

    8. Customer Requirements Maximum density, without sacrificing performance Give predictable performance Dont provide a feature thats unsuitable for production use

    9. Hyper-V R2 SP1 Dynamic Memory

    10. Dynamic Memory Goals Higher VM consolidation ratios with minimal performance impact Dependent on: How much variation in memory utilization the workloads have How good a job you did of sizing the systems in the first place Work well for both server and desktop workloads Add minimal overhead to the system Pass the that looks right test

    11. Adding/Removing Memory Adding Memory Enlightened fashion Synthetic Memory Driver (VSP/VSC Pair) No hardware emulation Light weight Removing Memory Wanted to remove memory Ballooning is more efficient Messes up task manager in the guest OS

    12. System Requirements Parent Requirements: Windows Server 2008 R2 SP1 Microsoft Hyper-V Server 2008 R2 SP1 Windows Server 2003, 2008 & 2008 R2 32-bit & 64-bit versions Windows Vista and Windows 7 Enterprise and Ultimate Editions only 32-bit & 64-bit versions

    13. Dynamic Memory Architecture & Concepts

    14. Obligatory Block Diagram

    15. Availability Availability is a concept How much memory does the VM have? How much memory does the VM want? The difference is the availability Availability shows how much RAM is free E.G. A virtual machine currently needs 780MB of RAM it has 900MB of RAM. This means that the availability is (900-780)/780 == 15.3% E.G. A virtual machine currently needs 1000MB or RAM it has 1200MB of RAM. This means that the availability is (1200-1000)/1000 = 20%

    16. Pressure Pressure is another way to talk about the memory state of the virtual machine Not used in the UI but is used in performance counters. Pressure == amount of memory the VM wants / the amount of memory the VM has Pressure of 1 (or 100%) means the VM has exactly what it wants Below 100% means there is free room Over 100% means that the VM is squeezed (high pressure)

    17. Memory Buffer How much free memory should we try and keep in the VM? Allows for responsiveness to bursty workloads Can be used for file cache I like to configure my virtual machines so that they have ~20% free memory

    18. Benjamin Armstrong Senior Program Manager Lead Microsoft Dynamic Memory DEMO

    19. System Impact

    20. Changes to Root Reserve Hyper-V has always had the concept of a reserve of memory that is kept for the parent partition DM allows VMs to push up against the reserve consistently New behavior to better protect the parent partition from rampaging virtual machines New registry key in place Allows you to reserve static memory for the parent partition HKLM:\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Virtualization\MemoryReserve May result in less memory being available for VMs

    21. Dynamic Memory System Impact Changes to NUMA Management Hyper-V tries to get all memory for a VM from a single NUMA node; when it cannot, the VM spans NUMA nodes Dynamic memory can result in more virtual machines spanning NUMA nodes; a VM might start all on one node but added memory might come from another node New option to disable NUMA node spanning makes the system behave like multiple small computers 21

    22. Memory Techniques / Competition

    23. Understanding philosophical differences Microsoft Understands what guest information to use Building on top of guest OS knowledge Trying to get the best bang for buck in virtual memory management VMware Does not trust guest information Building a black box solution Started with memory swapping, and digging out of the hole

    24. Dynamic Memory, not Overcommit Overloaded Term Page Sharing Second Level Paging Balloon Type Mechanisms No one wants to overcommit their resource You dont overcommit other resources (really you do not) VMware does not want you to overcommit memory (really) DM treats memory like we treat CPU resources Dynamically schedulable resource

    25. External Page Sharing How it works: Hash all memory and store it in a table Identify the common hashes and then Perform a bit by bit comparison What VMware doesnt tell you Page Sharing not dynamic Can take hours to share pages The largest benefit are zero pages Doesnt work with large pages

    26. Second Level Paging Many problems: Swapping Guest Kernel Resources Double Paging Disks are slow But it always works

    27. Other Techniques Memory compression Guest directed page sharing And on We will continue to invest here and work on identifying the best techniques for customer work loads

    28. What next?

    29. Test the beta and talk to us! Try Dynamic Memory out for both server and desktop environments Let us know how DM is working for you Let us know if you think we have something wrong

    30. Question & Answer Session

    31. Complete an Evaluation on CommNet and enter to WIN these prizes! <Prizes & Process TBC>

    32. Related Content SVR313 Windows Server 2008 R2 Hyper-V Performance Analysis: How You Can Get the Most out of Hyper-V SVR307 RemoteFX drilldown: What is it? How does it work? SVR315 Disaster Recovery and Virtualization Backup Best Practices SVR306 Networking and Windows Server 2008 R2 Hyper-V: Deployment Considerations

    34. Resources

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